Pathological Disorders of the CNS Involving Accumulation of Misfolded and/or Aggregated Proteins
For many decades, clinicians have been aware of the formation of insoluble protein aggregates in particular diseases. In Alzheimer disease (Selkoe, 1997, 2002), the presence in the CNS of β-amyloid-containing plaques is associated with neurodegeneration and dementia. Similarly, other neurodegenerative diseases have recently been discovered to involve protein aggregation in the brain. For example, prion diseases such as kuru, Creutzfeldt-Jacob disease and bovine spongiform encephalopathy are associated with amyloid deposits of the prion protein (PrP). Polyglutamine repeat diseases such as Huntington disease are likewise associated with neuronal cytosolic and intranuclear inclusions (DiFiglia et al., 1997). These inclusions are composed of fibrils that stain similarly to amyloid (Scherzinger et al., 1997). Finally, in Parkinson disease, inclusions known as Lewy bodies, found in the cytoplasm of cells of the basal ganglia, include amyloid-like aggregates of the protein α-synuclein (Conway et al., 2000; Serpell et al., 2000).
Huntington's disease (HD), identified in the late 1800s by the physician George Huntington, is an autosomal dominant neurodegenerative disease whose symptoms are caused by the loss of cells in the basal ganglia of the brain. This damage to cells affects cognitive ability (thinking, judgment, memory), movement, and emotional control. HD is characterized by uncontrollable, dancelike movements and personality changes. HD patients develop slurred speech, an unsteady walk and difficulty in swallowing. There is no effective treatment for HD. After a long illness, individuals with HD die from complications such as choking or infection.
In 1993, the mutation that causes HD was identified as an unstable expansion of CAG repeats in the IT15 gene encoding huntingtin, a protein of unknown function (Menalled and Chesselet, 2002). The CAG repeat expansion results in an increased stretch of glutamines in the N-terminal portion of the protein, which is widely expressed in brain and peripheral tissues (Gutekunst et al., 1995). The exact mechanisms underlying neuronal death in Huntington's disease remain unknown. Proposed mechanisms have included activation of caspases or other triggers of apoptosis, mitochondrial or metabolic toxicity, and interference with gene transcription. Recent advances in the understanding of the pathophysiology of neurodegenerative diseases in general and of Huntington's disease in particular, have suggested new therapeutic strategies aimed at slowing progression or delay onset of the neurodegenerative disease.
Alzheimer's disease (AD) is an irreversible, progressive brain disorder that occurs gradually and results in memory loss, behavioral and personality changes, and a decline in mental abilities. These losses are related to the death of brain cells and the breakdown of the connections between them. The course of this disease varies from person to person, as does the rate of decline. On average, AD patients live for 8 to 10 years after they are diagnosed, though the disease can last up to 20 years.
AD advances by stages, from early, mild forgetfulness to a severe loss of mental function. At first, AD destroys neurons in parts of the brain that control memory, especially in the hippocampus and related structures. As nerve cells in the hippocampus stop functioning properly, short-term memory fails. AD also attacks the cerebral cortex, particularly the areas responsible for language and reasoning Eventually, many other areas of the brain are involved.
Parkinson's disease (PD) is an idiopathic, slowly progressive, degenerative CNS disorder characterized by slow and decreased movement, muscular rigidity, resting tremor, and postural instability. Despite extensive investigations, the cause of PD remains unknown. The loss of substantia nigra neurons, which project to the caudate nucleus and putamen, results in the depletion of the neurotransmitter dopamine in these areas. Significant hints into PD pathogenesis have been yielded by the use of 1-methyl-4-phenyl-1,2,4,6-tetrandropyridine (MPTP), a neurotoxin that replicates most of the neuropathological hallmarks of PD in humans, nonhuman primates, and other mammalian species, including mice. Although the MPTP mouse model departs from human PD in a few important ways, it offers a unique means to investigate, in vivo, molecular events underlying the demise of midbrain dopaminergic neurons (Dauer and Przedborski, 2003).
Acute and/or chronic neuronal loss in the adult CNS results in the irreversible loss of function due to the very poor ability of mature nerve cells to proliferate and compensate for the lost neurons. Thus attenuating or reducing neuronal loss is essential for preservation of function. In most of the neurodegenerative diseases like Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis (ALS) and Huntington's disease, the etiology is not clear, hence they are incurable. Nevertheless, there are some primary and secondary risk factors, which are the target for therapeutic intervention aiming at inhibiting or attenuating progress of neuronal loss, collectively termed as neuroprotective therapy. Some of the risk factors are disease-specific but others, like excitatory amino acids, free radicals and nitric oxide, are common to all the neurodegenerative disorders. These factors are essential self-components in the healthy CNS, but with their accumulation in excess amounts in the degenerative tissue, they become cytotoxic leading to the spread of damage beyond the initial cause of neuron death.
Glutamate is one of the most common mediators of toxicity in acute and chronic degenerative disorders like status epilepticus, cerebral ischemia, traumatic brain injury, ALS, Huntington's disease, lathyrisms and Alzheimer's disease. Glutamate is a primary excitatory neurotransmitter in the human CNS. L-glutamate is present at a majority of synapses and is capable of displaying dual activity: it plays a pivotal role in normal functioning as an essential neurotransmitter, but becomes toxic when its physiological levels are exceeded.
In order to minimize neuronal loss (neuroprotection) several approaches have been adopted, at which the most common is targeting the risk factors in an attempt to neutralize or inhibit their action. Unfortunately, these therapeutic strategies showed marginal efficacy in human subjects with concomitant severe side effects. The failure of agents with discrete singular mechanisms of action argues for a multi-pronged approach.
Protective Autoimmunity
Loss of neurons in patients with devastating chronic neurodegenerative disorders is attributed to numerous factors, most of them (for example, oxidative stress, ion imbalance, metabolic deficits, neurotransmitter imbalance, neurotoxicity) common to all such diseases (Doble, 1999). Even those factors that are apparently unique to a particular disorder share certain common features, including changes in the extracellular deposition of self-compounds resulting in conformational and other changes, as well as in their aggregation, often culminating in plaque formation (Hardy and Selkoe, 2002).
The local immune response to injuries in the CNS has often been blamed for the progressive neurodegeneration that occurs after an insult (Hauben and Schwartz, 2003). Studies in the inventors' laboratory, however, have challenged the long-held notion that activated microglia or blood-borne activated macrophages contribute to the ongoing pathology, and suggest instead that these immune cells are harnessed to aid recovery, but may be unable to display a significant positive effect because they fail to acquire the necessary phenotype (activity) or because their intervention is not strong enough or is inappropriately timed. This suggestion was supported by the demonstration that, in rats, macrophages activated by peripheral nerve (Rapalino et al., 1998) or by skin (Bomstein et al., 2003) can be helpful in promoting recovery from spinal cord injury. The functional activity of such macrophages was recently found to resemble that of APC (Bomstein et al., 2003).
Subsequent studies by the inventors suggested that after a mechanical or biochemical insult to the CNS the local immune response, which is mediated by T cells directed against self-antigens residing in the site of the lesion (i.e., autoimmune T cells), determines the ability of the neural tissue to withstand the unfriendly extracellular conditions resulting from the injury. It thus seems that the body protects itself against toxic self-compounds in the CNS by harnessing a peripheral adaptive immune response in the form of T cells specific to antigens residing in the site of damage (Hauben et al., 2000a; Moalem et al., 1999a; Yoles et al., 2001; Schori et al., 2001a; Schori et al., 2001b). The T cells that mediate protection are directed not against a particular threatening self-compound but rather against dominant self-antigens that reside at the lesion site (Mizrahi et al., 2002; Schwartz et al., 2003; Bakalash et al., 2002).
Further studies by the inventors suggested that T-cell specificity is needed in order to ensure that among the T cells that arrive at the site, those encountering their specific or cross-reactive antigens (presented to them by local microglia acting as APC) will become activated. The activated T cells can then provide the necessary cytokines or growth factors that control the activity of the local microglia and the friendliness of the extracellular milieu (Schwartz et al., 2003; Moalem et al., 2000; Kipnis et al., 2000).
The concept of T cell-dependent “protective autoimmunity” has been formulated by the inventor Prof. Michal Schwartz and her group (Kipnis et al., 2002a; Schwartz and Kipnis, 2002a). According to this concept, an acute or chronic insult to the CNS triggers an autoimmune response directed against proteins residing in the lesion site. T cells homing to the lesion site are activated by cells presenting the relevant antigen. Once activated, they augment and control local immune cells, allowing efficient removal of toxic compounds and tissue debris, thus protecting the damaged nerves from further degeneration. The potential of the immune system to counteract the hostile conditions is enhanced by boosting the normal immune response. Based on this hypothesis, boosting the immune system with a suitable antigen should provide neuroprotection. Among suitable antigens identified by the present inventors is Copolymer 1.
Copolymer 1
Copolymer 1, also called Cop 1, is a random non-pathogenic synthetic copolymer, a heterogeneous mix of polypeptides containing the four amino acids L-glutamic acid (E), L-alanine (A), L-tyrosine (Y) and L-lysine (K) in an approximate ratio of 1.5:4.8:1:3.6, but with no uniform sequence. Although its mode of action remains controversial, Cop 1 clearly helps retard the progression of human multiple sclerosis (MS) and of the related autoimmune condition studied in mice, experimental autoimmune encephalomyelitis (EAE). One form of Cop 1, known as glatiramer acetate, has been approved in several countries for the treatment of multiple sclerosis under the trademark Copaxone® (Teva Pharmaceutical Industries Ltd., Petach Tikva, Israel).
Vaccination with Cop 1 or with Cop 1-activated T cells have been shown by the present inventors to boost the protective autoimmunity, after traumatic CNS insult, thereby reducing further injury-induced damage, and can further protect CNS cells from glutamate toxicity. Reference is made to Applicant's previous U.S. patent application Ser. Nos. 09/765,301 and 09/765,644 and corresponding published International Application Nos. WO 01/52878 and WO 01/93893, which disclose that Cop 1, Cop 1-related peptides and polypeptides and T cells activated therewith prevent or inhibit neuronal degeneration and promote nerve regeneration in the CNS or peripheral nervous system (PNS), and protect CNS cells from glutamate toxicity.
Prof. Schwartz and colleagues have shown that Cop 1 acts as a low-affinity antigen that activates a wide range of self-reacting T cells, resulting in neuroprotective autoimmunity that is effective against both CNS white matter and grey matter degeneration (Kipnis et al., 2002a; Schwartz and Kipnis, 2002a). The neuroprotective effect of Cop 1 vaccination was demonstrated by the inventors in animal models of acute and chronic neurological disorders such as optic nerve injury (Kipnis et al., 2000), head trauma (Kipnis et al., 2003), glaucoma (Schori et al., 2001b), amyotrophic lateral sclerosis (Angelov et al., 2003) and in the applicant's patent applications WO 01/52878, WO 01/93893 and WO 03/047500.
The use of Copolymer 1 for treatment of prion-related diseases is disclosed in WO 01/97785. Gendelman and co-workers disclose that passive immunization with splenocytes of mice immunized with Cop 1 confers dopaminergic neuroprotection in MPTP-treated mice (Benner et al., 2004).
All patents and patent applications cited herein are hereby incorporated by reference in their entirety as if fully disclosed herein.